| In recent years,with the rapid development of China’s urbanization,haze pollution and other air quality problems appear in more and more cities.Cities with good air quality,such as Xiamen,will also have mild haze pollution in winter.The new particle formation event has become one of the important sources of atmospheric particles.The research on the particle size distribution and the formation process of new particles in the urban atmosphere can further improve the understanding of the impact mechanism of the environmental and climate effects of particles,and provide scientific basis for the determination of the National Atmospheric Environment standard optimal pollutants.At present,there are relatively few studies on the change characteristics of fine particle size distribution and the influencing factors of new particle generation events in light pollution weather in China,which limits the further work of air pollution prevention and control.Therefore,based on the field observation results of the superstation of atmospheric environment observation of Xiamen Institute of urban environment,Chinese Academy of Sciences in winter 2019 and the comprehensive building of Anhui Institute of Optics and precision machinery,Chinese Academy of Sciences in Hefei in 2020 summer.This paper analyzes in-depth the particle size distribution characteristics,new particle formation events and their evolution rules of atmospheric fine particles under light pollution weather conditions.(1)This paper systematically summarizes the particle size distribution of atmospheric particles,the mechanism of new particle formation and the experimental results in typical areas,and presents the expressions of important parameters in the process of new particle formation,such as the new particle formation rate(Jdp)and the particle growth rate(GR).In view of the rapid increase of sub-3nm particle number concentration in the small particle size range,this paper proposes a new method for the calculation of high GR for 1～3nm particles.Based on Kernel equation and interpolation method,a new method is proposed with PSM saturation flow rate-particle size-detection efficiency curve.to improve the resolution of PSM in sub-3nm range.(2)The outdoor observation experiments of atmospheric particles in Hefei summer and Xiamen winter were designed and carried out.The particle size distribution and new particle formation events of atmospheric particles were comprehensively observed in the superstation of urban environment institute with PSM and SMPS particle size spectrometer,meteorological parameter measuring instrument and main air pollutant monitoring equipment.During the observation period,the average concentration of total atmospheric particles(7-300nm)in Hefei is(37.8 ± 0.2)× 104 cm-3,in which the proportion of Nucleation mode particles is about 23%,that of Aitken mode particles is about 57%,and that of accumulation mode particles is about 20%.The mean concentration of total fine particles in Xiamen is(46.9 ± 0.2)× 104 cm-3,in which the proportion of particles in Nucleation mode,Aitken mode and Accumulation mode is 33%,49%and 18%,respectively.Under the background of high concentration of fine particles(PM2.5 daily mean ≥35μg·cm-3),the concentration of total particles is(42.9 ± 0.2)× 104 cm-3,in which the proportion of particles in Nucleation mode,Aitken mode and Accumulation mode is 26%,51%and 23%respectively,and the particle size distribution showed double peaks of Nucleation mode and Aitken nuclear mode.Under the background of low concentration of fine particles(PM2.5 daily mean<35 μg·cm-3),the concentration of total fine particles is(54.0 ± 0.2)× 104 cm-3,which is 26%higher than that under the background of high concentration,the proportion of Nucleation mode particle is 38%,the proportion of Aitken nuclear mode is 48%,the proportion of Accumulated mode particle is 15%,,and the particle size distribution is a single peak of particles in Nucleation mode.Combined with the meteorological parameters,the source of fine particles in the observation area is analyzed.The results show that local emission is the main source of fine particles in Hefei in summer.New particle formation and local emission are the main sources of fine particles in Xiamen in winter.(3)The evolution characteristics of typical new particle formation events in Xiamen are analyzed.The characteristics of new particle formation and growth in the background of different concentrations of particles were analyzed and compared.During the observation period,the total frequency of new particle formation events was 21%.In the background of high concentration particles(PM2.5 daily average>35μg·cm-3),the frequency of new particle formation was 5%,the condensation pool level was 1.02×10-2·s-1,the average of new particle formation rate was 17.22 cm-3·s-1,and the average growth of particle size was 4.44 nm·h-1.The frequency of new particles formation in the background of low concentration particles(PM2.5 daily mean<35μg·cm-3)is 16%,which is three times of that in the background of high concentration;the average condensation sink is 0.72×10-2·s-1,which is 31%less than that in the background of high concentration;the average formation rate of new particles is 29.04 cm-3·s-1,which is 68%higher,and the average growth rate of particle size is 5.40 nm·h-1,which increase 22%.The results show that the clean weather is more conducive to the formation and growth of new particles.The influence of environmental humidity on the rate of new particle formation is different under different background particle concentrations.In light polluted weather,the rate of new particle formation increases with the increase of humidity.In clean weather,humidity and the rate of new particle formation change in the opposite direction.In the initial stage of new particle formation(1～25 nm),with the increase of particle size,the rate of new particle formation decreased and the rate of particle size growth increased.Combined with meteorological parameters and conventional pollution gas,the change of the number and concentration of particles in each mode in the event of new particle formation was analyzed.In both cases,the correlation coefficient between the number concentration of particles in Nucleation mode and humidity is negative.Under the background of high concentration of particles,the average correlation coefficients of the number of particles concentration and humidity in Aitken and Accumulation modes are 0.17 and 0.57,respectively.Under the background of high concentration of particles,the average correlation coefficients of the number of particles concentration and humidity in Aitken and Accumulation modes are-0.48 and 0.02,respectively.Under the background of high concentration,the effect of humidity on the growth of particle size is more obvious.In the process of new particle formation under the background of high concentration of particles,the concentration of SO2 and the concentration of three kinds of particles show a significant correlation,and the gas precursor of new particle formation is likely to be sulfuric acid.In the event of new particle formation in the background of low concentration of particles,the concentration increment of Nucleation mode particles and Accumulation mode particles is about twice as much as that in the background of high concentration,and there is no significant change in SO2 concentration at the same time.The new particle formation mechanism is different from that in the background of high concentration,which may be due to the participation of organic matter in the nucleation. |
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